Maternal immunoglubulins (Ig, antibodies) derived from colostrum are the single most important factor in protecting a neonatal focal from disease. Millions of dollars are spent annually on the treatment of foals which fail to attain adequate serum Ig levels. Many of these foals die even when vigorous treatment is instituted. Others never reach full potential due to debilitating infections.
Due to the mare's epitheliochorial placentation and separation of maternal and fetal circulations, transplacental transfer of material antibody does not occur. Foals must rely on adequate intake and absorption of colostral Ig for resistance to infectious diseases during the first few weeks of life. Ingestion of colostrum must occur soon after birth since the ability of the gut to absorb Ig is time dependent. An absorption rate of 100 percent at birth decreases to zero within 12 to 18 hours.
Low Ig concentration in mare colostrum has been incriminated as being the major cause of failure of passive transfer. However no commercial "on the farm" technique is available to assess Ig content in mare colostrum and estimation of Ig content by the appearance and consistency of colostrum can be misleading. Thick viscous samples may not be good indicators of quality. Test kits on the market measure serum IgG levels in foals greater than 18 hours of age, a time when no further absorption of Ig can occur.
We have found a linear relationship between colostral specific gravity and colostral Ig levels. This relationship served as the basis for the "colostrometer" which estimates Ig content of colostrum. The "colostrometer" has been field tested on Thoroughbred, Quarter Horse, Arabian and Standarbred farms and found to be a practical, rapid and accurate method for determining colostral IgG. The ability to detect low colostral Ig levels immediately postpartum will allow the farm manager or veterinarian to identify those foals at high risk for disease and supplement them with colostrum higher in IgG content.
Significant differentiation of a colostrum specimen occurs over a narrow range of specific gravity between 1.040 and 1.100. The test must be performed under field conditions thereby not allowing use of radio-immunodiffusion assays which would be used under laboratory conditions. The material is opaque, viscous, and adhesive. These factors, together with the limited sample volume, do not allow the use of conventional hydrometers or equivalent refractometer methods.